It is obvious that after a while the number of names continually swelling would become too great to be recited at once. It became necessary, therefore, to take some names on one day, others on another. And this originated the Necrologium, or catalogue of the dead. The custom of reading the diptychs has ceased to be observed in the Roman Liturgy, though we find it indicated there by the "Oratio supra Diptycha." At present, when the celebrating priest arrives at that part of the Canon called the "Memento," he secretly commemorates those for whose souls he more particularly wishes to pray. But, in addition to the diptychs of those for whom the priest and congregation were desired to pray, there was the catalogue of the Martyrs and Saints for whom the Church thanked God. For instance, in the modern Roman Mass, in the Canon we have this commemoration: "Joining in communion with, and reverencing, in the first place, the memory of the glorious and ever-virgin Mary, Mother of our God and Lord Jesus Christ; as also of Thy blessed apostles and martyrs, Peter and Paul, Andrew, James, John, Thomas, James, Philip, Bartholomew, Matthew, Simon and Thaddaeus; Linus, Cletus, Clement, Xystus, Cornelius, Cyprian, Laurence, Chrysogonus, John and Paul, Cosmas and Damian, and of all Thy Saints," etc. This is obviously a mere fragment of a commemoration of the Blessed Virgin, of the apostles, and then of the special Roman martyrs. The catalogue of the Saints to be remembered was long; there were hundreds of martyrs at Rome alone, and their names were written down on sacred diptychs especially appropriated to this purpose. Such an inscription was equivalent to the present ceremony of canonization. The term canonization itself tells the history of the process. It is derived from that part of the Mass called the Canon, in which occurs that memorial already quoted. On the day when the Pope, after a scrutinizing examination into the sanctity of a servant of God, formally inscribes him among the Saints, he adds his name at the end of those already enumerated in the Canon, after "Cosmas and Damian," and immediately reads Mass, adding this name at this place. Formerly every bishop could and did canonize--that is, add the name of any local Saint or martyr worthy of commemoration in his diocese. When the list became long, it was found impracticable to commemorate all _nominatim_ at once, and the Saints were named on their special days. Thus, out of one set of diptychs grew the Necrologium, and out of the other the Martyrology.